1. Field of the Invention
The invention relates to an electric power converter and, more particularly, to a series-parallel switching-type electric power converter that converts voltage between an output power line, connected to a load, and two batteries and that switches between a series mode in which electric power is converted between the output power line and the two batteries while the two batteries are connected in series with each other and a parallel mode in which electric power is converted between the output power line and each of the batteries in parallel with each other.
2. Description of Related Art
In a hybrid vehicle, an electric vehicle, or the like, that uses a rotary electric machine as a drive source, direct-current power of a battery is converted to alternating-current power by an inverter, and the rotary electric machine is driven by the alternating-current power. An electric power converter is provided between the battery and the inverter. The electric power converter steps up or steps down direct-current voltage.
Japanese Patent Application Publication No. 2012-070514 (JP 2012-070514 A) describes a configuration in which the function of an electric power converter is extended. This configuration has a series mode and a parallel mode for converting voltage between an output power line, connected to a load, and two batteries. In the series mode, electric power is converted between the output power line and the two batteries while the two batteries are connected in series with each other. In the parallel mode, electric power is converted between the output power line and each of the batteries in parallel with each other.
Japanese Patent Application Publication No. 2013-013234 (JP 2013-013234 A) describes a configuration that reduces a loss of an electric power converter by, in the parallel mode of JP 2012-070514 A, setting a phase difference between pulse width modulation (PWM) signals in two step-up circuits to 180 degrees.
As in the case of JP 2013-013234 A, at the time of reducing the loss of the electric power converter in the parallel mode, it is desirable to reduce a switching loss of a specific switching element of which generation of heat is intended to be suppressed, without limiting the output characteristic of the electric power converter.